Messages in this thread | | | Date | Mon, 10 Nov 2008 09:19:21 -0500 (EST) | From | Mikulas Patocka <> | Subject | Re: Queue upcall locking (was: [dm-devel] [RFC][PATCH] fix dm_any_congested() to properly sync up with suspend code path) |
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On Mon, 10 Nov 2008, Christoph Hellwig wrote:
> On Mon, Nov 10, 2008 at 08:11:51AM -0500, Mikulas Patocka wrote: > > For upstream Linux developers: you are holding a spinlock and calling > > bdi*_congested functions that can take indefinite amount of time (there > > are even users reporting having 50 disks in one logical volume or so). I > > think it would be good to move these calls out of spinlocks. > > Umm, they shouldn't block that long, as that completely defeats their > purpose. These functions are mostly used to avoid throwing more I/O at > a congested device if pdflush could do more useful things instead. But > if it blocks in those functions anyway we wouldn't have to bother using > them. Do you have more details about the uses cases when this happens > and where the routines spend so much time?
For device mapper, congested_fn asks every device in the tree and make OR of their bits --- so if the user has 50 devices, it asks them all.
For md-linear, md-raid0, md-raid1, md-raid10 and md-multipath it does the same --- asking every device.
If you have a better idea how to implement congested_fn, say it.
Mikulas
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